IB were ruffled a few feathers (about $26 million) by FINRA in August 2020 when they were found to have failed to maintain an adequate anti-money laundering (AML) program, so one can imagine their compliance department has been walking on eggshells since then.
That can't be justified to lose even further customers. All other brokers have very little process for account opening, while IB makes it very complicate